Facebook CEO Mark Zuckerberg apologized for the data scandal that has roiled the social media network this week.

Zuckerberg said “I’m really sorry that this happened” in an interview to CNN, which aired hours after he and the social-media network’s No. 2 exec, Sheryl Sandberg, spoke up about the Cambridge Analytica data scandal.

The matter has roiled Facebook this week, after it was revealed that the British data firm inappropriately vacuumed up information from some 50 million Facebook users.

Both Zuckerberg and Sandberg acknowledged “mistakes” on the part of Facebook, but for some of their critics, the remarks fell short.

The scandal has contributed to a 10% drop in Facebook’s stock since last Friday.

Facebook CEO Mark Zuckerberg said “I’m really sorry that this happened,” in his first interview on the massive Cambridge Analytica data scandal that has roiled the social media network this week.

Zuckerberg made that admission on CNN Wednesday night, hours after he and COO Sheryl Sandberg issued their first statements on the matter.

“This is clearly a mistake in retrospect,” Zuckerberg said of the data-access rules that the British data firm exploited to vacuum up the data of some 50 million Facebook users.

Cambridge Analytica is being scrutinized for the methods it used during the 2016 presidential election, after executives with the firm boasted about their ability to covertly target voters, entrap politicians, and launch propaganda campaigns. The reach of those operations was multiplied by social-media platforms like Facebook.